For a period of several years, continuing efforts have been maintained to safeguard valuable documents and other objects against counterfeits and misuse. One such effort has involved producing specific forms of objects that are exceedingly difficult or impractical to duplicate. As a related cosideration, such objects must be recognizable for their identifiable characteristic. In that regard, it has been proposed to sense the identifying characteristic of an object, reduce the characteristic to a manageable data format and record such data on the object as a so-called "escort memory". For example, U.S. Pat. No. 4,423,415 (Goldman) discloses utilizing the inherent random characteristic of bond paper to identify individual documents. In another arrangement, U.S. Pat. No. 4,114,032 (Brosow et al.) discloses embedding magnetizable particles, e.g. fibers, in documents to accomplish an identifiable characteristic. Various other schemes for characterizing objects including documents have been proposed. However, a continuing need exists for alternative and improved forms of such systems to accommodate the needs of economy and expediency.
Magnetic materials have been developed as effective mediums to record data. Magnetics are generally inexpensive and relatively immune from dirt and small scratches. In general, the present invention is based on recognizing certain random characteristics of magnetic medium and utilizing such characteristics as a basis for identification. For example, magnetic medium may be printed or otherwise disposed on a base or substrate sheet of paper or paper-like medium, to impart random magnetic characteristics that may be repeatably sensed to identify an object. An effective form of document identification is disclosed herein utilizing a repeatably sensible, random characteristic of a magnetic substrate deposited on a document. The document also carries data indicative of the characteristic that may be used for verification by comparison.
In accordance with one technique of the present invention, a base member, e.g. paper, provides a support substrate surface on which a layer of magnetic substance is disposed to possess a repeatably sensible, random characteristic. The magnetic substance may vary as a result of: nonuniformity of the paper surface, nonuniformities in printing or other deposition process, or variations in the dispersion of magnetic particles. Thus, density variations are randomly created that uniquely characterize an individual document and furthermore are fixed and repeatable. The random characteristic is sensed and may be recorded on the document as with a magnetic stripe as well known in the prior art. Of course, other machine-readable indicia as optical codes may also be utilized. In any event, such a document may be verified or authenticated by freshly sensing the random magnetic characteristic, reducing it to a data format as before, and comparing the result with the recorded data format. In accordance herewith, various production and verification systems are disclosed and in that regard specific sensing techniques are set out.
As disclosed in detail below, the system hereof may be variously implemented using different forms of magnetic medium, different support substances and different production and utilization techniques. For example, the random magnetic characteristic may be accomplished by printing a document with varying magnetic materials. Also, various techniques may be employed to precondition and sense the magnetic layer for comparison.